Not Applicable
Not Applicable
1. Field of the Invention
The invention relates to the technical field of vehicle steering columns.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98;
Steering column conventionally designates a tubular element, fixed to the body of the vehicle, under the dashboard, which guides and supports the transmission shaft connected to the steering wheel.
This steering wheel is then a manual control apparatus, connected to the steered wheels and used by the driver to steer the vehicle.
The invention also concerns decoupled steering columns. Unlike conventional steering columns, decoupled steering columns are not associated with a steering box converting the circular movement of the steering wheel into angular displacement of the steering arm which causes wheel turning.
On the contrary, for these instances of decoupled steering, there is no direct mechanical connection between the steering wheel and the wheels resting on the ground, whether the vehicle is real or belongs to a simulation system.
This simulation can be a play object, connected with training in driving schools, or connected with interactive driving simulation for the requirements of motor vehicle manufacturers.
In such simulators, the reconstruction of forces at the steering wheel by means of a mechanism generating a resistive torque on the steering wheel as a function of the vehicle type to be simulated, equipped or not with power steering, must take into account the driving conditions to be recreated.
Measurement of the torque applied to the steering wheel is consequently essential for providing a good simulation, in real time.
Measurement of torque on the steering wheel shaft is also very important in servo steering or power steering.
This is because the level of assistance depends notably on the torque applied by the driver on the steering wheel.
The torquemeter, or torque sensor, used in servo steering gives out a signal indicative of the turning torque exerted by the driver on the steering wheel and therefore on the transmission shaft of the vehicle steering column.
This signal is conventionally sent to a steering assistance computer which controls the assistance, by controlling for example an electric motor, in the case of electric servo steering.
The invention relates more particularly, but not exclusively, to steering columns having a magnetic pulse generator referred to as a xe2x80x9ccoderxe2x80x9d and a functionally associated detection device referred to as a xe2x80x9csensorxe2x80x9d of magnetoresistance or Hall effect probe type.
Here, xe2x80x9cHall effect probexe2x80x9d designates sensors comprising at least one sensitive element, generally a semiconductor in wafer form, such that, when a current I passes through it, being furthermore subjected to an induction B making an angle xcex8 with the current, there appears, in a direction perpendicular to the current I and to the induction B, a voltage V having the value V=K.I.B. sin xcex8, K being referred to as the xe2x80x9cHall constantxe2x80x9d, and being characteristic of the material and geometry of the sensitive element, K varying with temperature.
Here, xe2x80x9cmagnetoresistancexe2x80x9d designates a varistor sensitive to the intensity of a magnetic field, in other words a resistance made of semiconductor material whose ohmic value varies with variation in the intensity of a unidirectional magnetic field applied perpendicular to the direction of the current passing through the resistance.
Hall probes are considered as active sensors, since the information delivered is connected with an electromotive force.
When these Hall probes are used for the translation of movement, the magnet which creates the induction is associated with the sensing body acted on by the primary value to be measured, modifying the secondary measurand, namely conventionally the normal component of the induction, the measurand to which the probe is directly sensitive.
Devices are known for measuring the torque exerted on a shaft comprising a sensor, for example a Hall effect sensor, positioned at air gap distance from a magnetic pattern with a rapid transition, so that the sensor measures the variation in magnetic induction of the coder and, by means of an electronic circuit, the torque exerted is then deduced therefrom.
For example, in such devices, the coder is immovably attached to a part of the steering column which, under the action of the exerted torque, moves with respect to a substantially non-stressed part with which the sensor is associated.
Such devices have the following drawbacks:
the sensitivity of the sensor can vary as a function of the temperature. This is because it takes into account the drift of the sensor and the magnets. Certain correction principles consist of using a Hall effect sensor partially compensating for the temperature drift of the magnets or appropriate processing electronics. This principle has limited performance in view of the random sensitivity and offset drifts of the sensors;
a magnetic shielding device must be used in order to be free from any external magnetic perturbation;
the sensitive elements must be skilfully positioned opposite the magnetic transition in order to minimize the magnetic offset, and the drift of the zero with regard to temperature which results therefrom.
The invention relates to a steering column provided with means of measuring the torque based on electromagnetic phenomena which does not have the drawbacks of the devices of the prior art.
To that end, the invention proposes a vehicle steering column having a manual control apparatus for applying a torque to the transmission shaft of the column, said column being provided with means of measuring the torque applied to said transmission shaft, the means of measuring the applied torque comprising a means generating magnetic pulses and a device for detecting these pulses, in which the detection device comprises a plurality of aligned sensitive elements chosen from amongst the group comprising Hall effect probes, magnetoresistances, and giant magnetoresistances, the sensitive elements being placed equidistant from one another.
The magnetic pulse generating means comprises a number of pairs of magnetic poles with reverse direction of magnetization of a given pole with respect to those contiguous with it, capable of providing, at the air gap under consideration, a sinusoidal magnetic field over the whole measurement area. For example, the number of pairs of magnetic poles is equal to at least two.
The detection device detects the relative movement between the sensitive elements and the magnetic pulse generating means.
In a first embodiment, the detection device comprises an even number 2N of sensitive elements. The even number of sensitive elements can be selected by programming of EEPROM, ZENER ZAPPING or equivalent type.
The set of 2N sensitive elements is divided into two subsets of N elements, each sensitive element of the first subset being connected to a first adder, each sensitive element of the second subset being connected to a second adder, the output S1 issuing from the first adder and the output S2 issuing from the second adder, via an inverter, are connected to the input of a third adder, and the signal COS=S1-S2 thus obtained is processed by a circuit, so as to deduce the torque exerted on the steering column.
In another embodiment, the detection device comprises a number of sensitive elements which is a multiple of four.
The set of 4P sensitive elements is divided into four subsets of P elements,
each sensitive element of the first P-element subset being connected to a first adder supplying a signal S1;
each sensitive element of the second P-element subset being connected to a second adder supplying a signal S2;
each sensitive element of the third P-element subset being connected to a third adder supplying a signal Sxe2x80x21;
each sensitive element of the fourth P-element subset being connected to a fourth adder supplying a signal Sxe2x80x22;
a circuit of adders and inverters supplying two signals SIN and COS respectively having the values:
SIN=(S1xe2x88x92S2)xe2x88x92(Sxe2x80x21xe2x88x92Sxe2x80x22);
COS=(S1xe2x88x92S2)xe2x88x92(Sxe2x80x21+Sxe2x80x22);
these signals SIN and COS being connected to a fifth adder, the signal SCOUPLE=SIN+COS thus obtained being processed by a circuit, so as to deduce the torque exerted on the steering column.
A programmable gain G is possibly applied to the signal COS and/or the signal SIN before being connected to the fifth adder, the gain G being programmed so as to obtain a zero signal SCOUPLE when the torque applied to the column is zero.
In a supplementary embodiment, the signals issuing from each sensitive element are connected to a maximum intensity detector which, via a regulator and a control device, controls the sensitivity of the sensitive elements, so as to obtain a detection of the torque exerted on the steering column substantially independent of temperature.
In a variant, the sensitive elements are integrated on an ASIC type circuit support and the detection device can also be included in an ASIC type customized integrated circuit.
The magnetic pulse generating means are immovably attached to a part of the steering column which is deformed under the action of the exerted torque and the detection device is immovably attached to a substantially non-stressed part of the steering column.
Other objects and advantages of the invention will emerge in the course of the following description of one embodiment, said description being produced with reference to the accompanying drawings in which: